This invention relates to retaining rings used to contain centrifugal forces experienced by field winding end turns in a generator.
During normal operation, heat is produced in a generator due to the copper, iron, windage, load or other losses. A ventilation/cooling system is used to remove such generated heat sufficiently to insure the reliable operation of the generator. The objective of the ventilation/cooling system is to achieve relative uniform temperature distribution in the generator with low power consumption. However, due to the complexity of the generator geometry and heat generation, hot spots may exist in certain locations. For air or hydrogen cooled generators, the ventilation flow field at the gap entrance between the generator stator and retaining ring has drawn special attention, since it can result in large ventilating windage loss.
Retaining rings are typically mounted around the end portion of the rotor to enclose the field winding end turns of the generator. In conventional practice, these retaining rings are designed to have a substantially cylindrical shape, with a flat outer profile. This conventional retaining ring design can, however, result in a large pressure drop across the stator-rotor gap entrance and high drag force against the cooling flow, thus leading to a lower generator cooling efficiency. More specifically, conventional retaining rings with flat outer profiles form part of a flow bottleneck at the cooling flow entrance to the gap between the stator core and the rotor. In addition, the interface of the retaining ring nose and the rotor core forms a backward facing step. As cooling gas passes the stator-rotor gap entrance, it generates a large flow recirculation at the retaining ring nose. This results in a large pressure drop at the gap entrance.